Helicopter



FIG. 1 is a right side view of a helicopter;

FIG. 2 is a perspective right side view of the helicopter;

FIG. 3 is a left side view of the helicopter;

FIG. 4 is a perspective left side view of the helicopter;

FIG. 5. is a front view of the helicopter; and,

FIG. 6 is a rear view of the helicopter.

Broken lines, if any, are for illustrative purposes only and form no part of the claimed design. 

The ornamental design for a helicopter, as shown and described. 